Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Such information may comprise characteristics of the earth formations traversed by the borehole, along with data relating to the size and configuration of the borehole itself. Collecting and processing data during the drilling process allows the driller to make modifications or corrections to increase performance while reducing down time of the drilling process. Methods of measuring conditions downhole, including the movement and location of the drilling assembly contemporaneously with the drilling, have come to be known as “measurement-while-drilling” techniques, or “MWD.” Similar techniques, concentrating more on the measurement of formation parameters, have been referred to as “logging-while-drilling” techniques, or “LWD.” While distinctions between MWD and LWD may exist, the terms MWD and LWD are often used interchangeably. For purposes of this disclosure, the term MWD will be used with the understanding that this term encompasses both the collection of formation parameters and the collection of information relating to the movement and position of the drilling assembly.
In MWD operations, sensors and/or transducers on the drilling assembly continuously or intermittently monitor drilling parameters and formation data, and transmit the information to the surface as telemetry. A widely used telemetry system in MWD applications uses pressure pulses impressed on the drilling fluid (sometimes referred to as mud) within the drill string, and thus is known as mud pulse telemetry. In particular, mud pulse telemetry systems communicate by way of pressure pulses in a drilling fluid circulated under pressure through the drill string during drilling operations. The pressure pulses propagate from near the drill bit to the surface, where the pressure pulses are detected, and the data encoded therein extracted. Depending on the type of drilling fluid used, the velocity of the pressure pulses may vary between approximately 3000 and 5000 feet per second. The rate of transmission of data, however, is relatively slow due to pulse spreading, distortion, attenuation, modulation rate limitations, and other disruptive forces, such as ambient noise in the drill string. In most applications of mud pulse telemetry, the data rate at which information is sent from downhole to the surface (or vice versa) is about one Boolean value per second.
With recent developments in sensing and steering technologies available to the driller, the amount of data that can be conveyed to the surface in a timely manner using mud pulse telemetry is inadequate. Thus, systems and methods are needed to increase the data rate for telemetry between downhole and the surface, particularly in offshore applications.